Project Summary In the previous cycle we characterized the ability of certain benzodiazepines, in cooperation with decreased extracellular pH, to regulate airway smooth muscle (ASM) signaling and function via activation of the proton- sensing G protein-coupled receptor (GPCR) OGR1 (Ovarian cancer G-protein coupled receptor 1 aka GPR68). Importantly, we discovered that the multiple signaling pathways activated downstream of OGR1 could be selectively activated (i.e., biased) to produce differential effects on ASM contraction and proliferation. In this second cycle we propose to: 1) delineate the mechanisms by which the biasing of OGR1 signaling occurs; 2) detail an additional, mitochondrial-dependent effector arm of benzodiazepines that also inhibits ASM contraction; and 3) employ modeling to develop more efficacious benzodiazepine-like drugs that target these mechanisms. These goals will be achieved through 3 Specific Aims. In Aim 1 we will employ cell-based and integrative models of ASM contraction to clarify the how different benzodiazepines promote specific OGR1- and peripheral benzodiazepine receptor- signaling to regulate ASM contraction. In Aim 2 will establish the mechanistic basis of biased OGR1 signaling by assessing structure-function properties of OGR1 that dictate G protein coupling, and the biasing function of arrestins. In Aim 3 in collaboration with Core A we will employ molecular modeling to design new allosteric modulators to bias OGR1 signaling towards Gs/cAMP/PKA pathway activation and the associated therapeutic benefits, using the signaling and functional assays employed in Aims 1 and 2 to guide development and identify the most efficacious drugs. By establishing mechanisms mediating qualitative signaling by OGR1 and developing new agents that optimally bias OGR1 and promote bronchodilation, we will significantly advance the fields of both receptor biology and asthma therapeutics.